The present disclosure generally relates to depth sensing, and specifically relates to fast scanning large field-of-view devices for three-dimensional depth sensing.
To achieve a compelling user experience for depth sensing when using head-mounted displays (HMDs), it is important to create a dynamic and all solid-state light scanning device with both ultrafast scanning speed (e.g., MHz) and a large field-of-view. Usually, there are tradeoffs between speed, field-of-view and real-time reconfigurable illumination characteristics. Typically, a microelectromechanical system (MEM) with a mechanical based mirror device is used for scanning. However, the mechanical based mirror device has stability issues and has a limited scanning speed. In addition, the mechanical based mirror device is not reconfigurable in real time applications.
Most depth sensing methods rely on active illumination and detection. The conventional methods for depth sensing involve mechanical scanning or fixed diffractive-optics pattern projection, using structured light or time-of-flight techniques. Depth sensing based on time-of-flight uses a MEM with a mechanical based mirror device (scanner) to send short pulses into an object space. The depth sensing based on time-of-flight further uses a high speed detector to time-gate back-scattered light from the object to create high resolution depth maps. However, the mechanical based scanner performs inadequately in scanning speed, real-time reconfiguration and mechanical stability. The scanning speed is limited to a few kHz in the fast axis and a few hundred Hz in the slow axis. In addition, the mechanical based scanner has stability and reliability issues. Depth sensing based on a fixed structured light uses a diffractive optical element to generate a fixed structured light projected into an object space. The depth sensing based on the fixed structured light further uses a pre-stored look-up table to compute and extract depth maps. However, the depth sensing based on the fixed structured light and the diffractive optical element is not robust enough for dynamic depth sensing.